1. Field of the Invention
The present invention relates generally to instrumentation of the character used in respiratory diagnostic procedures and respiratory therapy in the field of medicine. More particularly the invention concerns a new and improved aerosol inhalation apparatus that generates sub-micron size radioactive particles for use in performing ventilation studies of the lungs.
2. Discussion of the Prior Art
Various diagnostic procedures involving radioactive materials have been in use for many years in the study of lung functioning. One such procedure involves the injection of Macro-aggregated albuminum (MAA) tagged with radioactive Technetium (Tc.sup.99m). These particles when trapped in the lungs can be imaged externally with an instrument known as a Nuclear Scintillation Camera, and the resulting images used to determine if any area of the lungs are not functioning properly. In the event of depiction of malfunctioning areas, a question often arises as to whether the cause is due to some type of chronic respiratory disease, or if it is caused by blockage due to emboli. A lung ventilation study is often performed to assist the physician in the differential diagnosis of pulmonary embolism, and to aid in the evaluation of small airway disease.
Historically, ventilation studies have been performed with the use of radioactive gases such as Xenon-133, Xenon-127, and Krypton-81m. More recently techniques have been developed whereby liquids tagged with a radioactive material such as Tc.sup.99m can be aerosolized and breathed into the patient's lungs for distribution assessment with scintillation camera imaging. The primary advantage of the aerosol procedure over the use of a radioactive gas is that particles in the aerosol mist are trapped in the lungs rather than being totally exhaled, thereby allowing the imaging of the lungs from various anatomical positions. Disadvantageously, with the radioactive gas method, only one view (usually the posterior) can be taken.
General acceptance of the radioaerosol technique for lung ventilation studies was substantially delayed due to the unavailability of radioaerosol generator-delivery systems designed specifically for diagnostic lung imaging. If particle sizes are large, for example, greater than approximately 2 micron, hyperdeposition of aerosol in the trachea and major airways in patients known to be free of airway obstruction is observed. Also, if particle sizes are large, deposition in the extremities of the lungs is minimal, causing poor visualization on the scintillation camera images. In an attempt to overcome these problems the addition of a "settling bag", was suggested by Dr. George Taplin in the late 1970's. In accordance with this approach, a radioaerosol mist was produced whereby most particles larger than 2 microns were removed. This development resulted in a much wider acceptance of the radioaerosol ventilation study technique. More recently, commercial production of nebulizers producing particle sizes in the range of 1-2 micron have further popularized the general procedure.
An additional refinement called "Pseudogas" was developed in Australia in 1985 and is now undergoing trials at one or more medical institutions here in the United States. This refinement is discussed in an article entitled "Lung Ventilation Studies with Technetium-99m Pseudogas". Journal of Nuclear Medicine. 27:842-846, 1986. Although produced only through use of very expensive instrumentation, Pseudogas is receiving very favorable clinical review in that it provides better visualization of the lung periphery with evidence of reduced central airway trapping. In this case, particle size is 0.12 micron diameter which is a order of magnitude smaller than conventional aerosols.
The apparatus of the present invention constitutes a substantial improvement over existing radioaerosol devices providing particle sizes on the order of 0.3 micron, Mass Media Aerodynamic Diameter (MMAD), thereby approaching the particle sizes produced by the "Pseudogas" generator. Although producing particle size approaching that of "Pseudogas", the device of the present invention is an inexpensive, easy to use, multipurpose application unit.